Laser frequency offset locking using electromagnetically induced transparency

The authors have used an electromagnetically induced transparency resonance in rubidium as a dispersive reference to lock the relative frequency of two lasers to the atomic ground-state hyperfine splitting. The beat frequency between the two lasers directly generates a microwave signal at 3.036 GHz (Rb-85) or 6.835 GHz (Rb-87). High bandwidth (600 kHz) feedback was achieved with only low-frequency (10 MHz) electronics using the frequency modulation sideband method. The spectral width of the microwave beat frequency was reduced to less than 1 kHz. The technique offers a convenient and low-cost method suitable for many topical two-frequency experiments, including coherent population trapping, slow light, lasing without inversion, and Raman sideband cooling. (c) 2007 American Institute of Physics.